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<html><head><title>Building a Concert Classical Guitar - Rosette</title>

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<h1>The Rosette</h1>

<p>According to an article by <a href="http://???">Trevor Semple</a>, wood mosaics have been created in England, in the area of the Tunbridge Wells, long before they were used on guitars. </p>

<p>The steps in creating a rosette are the following:</p>

<ul>
<li>1. Create a colored pattern on grid paper.</li>
</ul>

<p>A spreadsheet program, such as MS Excel or OpenOffice <investivate>Calc </investivate></investivate> can be used. With a few home bewed scritps, it is quite easy to play with the backgrount color of the cells..</p>

<ul>
<li>Calculate the amount and dimensions of strips you need.</li>
</ul>

<ul>
<li>Bring the veneer strips to the exact same thickness.</li>
</ul>

<p>This is a very important step, but can be very tricky. It ensures that all dots have the same height. If not done properly, the tile pattern will be slightly irregular.</p>

<p><a href="http://www.lie-nielsen.com/inlay-tools/">Lee Nielsen</a> has a veneer thicknesser  for this purpose. Sanding block and a scraper are also good for the job. A drum sander appears to be of less help, especially for very thin veneers.</p>

<p>If you have difficulties to thickness the whole veneer sheets, it may be useful to carry out the next step first. Especially if you use the Lie Nielsen thicknesser:</p>

<ul>
<li>Cut the veneer pieces to strips of the desired width and length.</li>
</ul>

<p>These strips of wood are then combined to create the vertial patterns:</p>

<ul>
<li>Create a stack of veneers for each unique vertical line (column sticks)</li>
</ul>

<ul>
<li>Glue the column sticks and clamp then all at once between pieces of lumber.</li>
</ul>

<p>This will assure that all columns will have the same height. <a href="http://www.connorguitars.com/images2/links_tips/connor_guitar_rosette05.jpg" target="_blank">Here</a> is an image from Connor guitars.</p>

<p>Make sure that the glue is distributed sparse and evenly. It may be useful to thin the glue a little bit.</p>

<p>For ease of handling while sawing, it is a good idea to glue the column stacks on a piece of lumber of the same height.</p>

<ul>
<li>Plane the side(s) of column sticks square.</li>
</ul>

<ul>
<li>Cut the column strips from the stick.</li>
</ul>

<p>If possible, cut the desired width as exact as possible, but <em>do not undercut</em>. Use a fine saw for length cuts, perhaps a gents saw, or a japanese dozuki.</p>

<ul>
<li>Bring the column strips to the exact same width and taper.</li>
</ul>

<p>This can be done with a long sanding block, or once again with the veneer thicknesser.</p>

<p>As the columns will have a very slight trapezoid shape, it may be usefull to introduce a slight taper to the sides, especially if the tiles are wide. This extra care helps to create a smooth, circular pattern. If omitted, the pattern may appear segmented. It can be done with a scraper, after thicknessing. Just scrape on the smaller end, leaving the wider end untouched. </p>

<p>A modified version of the veneer thicknesser, with blades at the desired tilt angle, may also work well. First cut the side, then cut the other. Note that the tilt angle of the blade for the second pass must be doubled...</p>

<p>A a result, you get column strips with the desired trapezoid shape.</p>

<ul>
<li>Glue the column strips to form a log of tiles.</li>
</ul>

<p>Make sure that the glue is distributed sparse and evenly. It may be useful to thin the glue a little bit.</p>

<ul>
<li>Clamp the tile log while the glue sets.</li>
</ul>

<p>Problem here: The sides of this stack are not square, and the inner column strips might slip out a little bit when simply clamped sideways. Two properly angled cauls (1 and 2) are required to create the side pressure on the tile strip (5). Additionally,you will need some pressure from top and bottom to prevent this. </p>

<p>Allan Chapman uses a set of slabs made of <a href="http://en.wikipedia.org/wiki/Corian">Corian</a>, a material invented by DuPont which does not stick to water-based glues, arranged in the following configuration:</p>

<p class="imgbox"><a name="rosette-fig-002"></a><img width="300px" src="fig-002.png" /><br/>Figure 2: Clamping the Tile Strip</p>
 
<p>Alternatively, the surfaces can be waxed or covered with wax paper to protect the cauls from sticking to the glue.</p>

<p>The side slabs (1 and 2) are cut at the angle dictated by the tile width, and provide the side pressure. The top and bottom slabs (3 and 4) prevent that the column strips in the tile log slip out. This method implies that the side slabs (1 and 2) are planed to the exact pattern height of the tiles. As an alternative, the column strips could be made longer as necessary to match the slab thickness. The the tile log must then be planed down to the desired height after the glueing step.</p>

<p>To save some material, the side slabs can be composed of wood (1a, 2a) and smaller pieces of Corian (1b, 2b). In any case, cut the corean slabs lengthwise at the exact tile side angle. For clamping, turn one of the piece around, and there you have the perfect angled side clamp slabs.</p>

<p>Glue squeeze-out: To address the glue squeeze-out while clamping the tile log, the top and bottom slabs (3, 4) can be slotted across. Then the glue that come out at the top and the bottom of the tile log (5) can flow sideways through the grooves, and does not lift the top and bottom slabs (3, 4).</p>

<p>Yet another idea: Bottom and top surface should be padded with cork to allow glue squeeze-out to go somewhere. Surfaces should be covered with wax, or wax paper, to avoid sticking when the arrangement is disassembled after the glue has set.</p>

<p>Let the glue set properly. Then dismantle the arrangement, and clean the tile log. Next step:</p>

<ul>
<li>Adjust the sides of the stick to the exact width and trapezoid shape.</li>
</ul>

<p>Although the individual column strips already have been tapered, the glue seams might have introduces inaccuracies, which are corrected with this step. If you refrained from tapering the individual column strips in the previous phase, this step is a must.</p>

<ul>
<li>Adjust the height of the tile log.</li>
</ul>

<p>If the column strips have been given additional material to top in the second step, the tile log must be planed to the exact height given by the plans.</p>

<p>The next step is somewhat optional, but I blieve it makes it easier to fit the tiles into the groove in the soundboard.</p>

<ul>
<li>Round off the top and bottom of the tile stick so that the tiles match the inner and outer diameter of the circle.</li>
</ul>

<p>This can be done with a shaped scraper or a radiused sanding block.</p>

<p>Some makers don't do it, since by the use of a circle cutter for creating the grooves for the purflings around the marquetry tiles brings the inner and outer border back to a perfect circle.</p>

<ul>
<li>Cut off tiles from the stick.</li>
</ul>

<p>Make sure to cut the pieces to the same thickness, if possible.</p>

<ul>
<li>Cut the channel for the tiles into the top.</li>
</ul>

<p>Use a circle cutter with a sharp tipped blade for this job. Perfect sharp edges facilitate inlaying the tiles.</p>

<p>Use a router plane or a chisel to dig out the wood. Make shure not to go too deep - the material is quite thin... </p>

<ul>
<li>Do a test fit of tiles into the channel.</li>
</ul>

<p>At this step, you have enough time to make fine corrections with sandpaper.</p>

<ul>
<li>Glue the tiles into the channel.</li>
</ul>

<p>Hide glue seems to be the material of choice here, because of the fast settling time. Additionally, it is possible to re-soften the glue with heat and steam to make corrections.</p>

<ul>
<li>If necessary, press down the tiles while the glue sets.</li>
</ul>

<p>A cork supplement may help to even out the differences in tile height. A piece of wax paper prevents the caul from sticking to the rosette. Let the glue set for a couple of hours. Then...</p>

<ul>
<li>Plane and scrape the tiles to a uniform height, but not down to the soundboard.</li>
</ul>

<p>The next step creates the purflings aound the marquetry tiles.</p>

<ul>
<li>Create the groove with a sharp circle cutter.</li>
<li>Dig the groove with a small router plane or a small sharp chisel.</li>
<li>Heat-bend the purfling strips to prevent them from breaking.</li>
<li>Test-fit the purfling strips, and make the necessary thickness corrections.</li>
<li>Glue the purflings into the channel.</li>
<li>Apply light pressure while the glue sets.</li>
</ul>

<p>Hide glue may be a problem here, since the glue sets very fast when cooling down. But with a</p>


<h2>Things to Consider</h2>

<p>1. Glue swells wood. You may have perfectly thicknessed purflings to go into a perfecly sized groove. But in practice, it is advisable to undersize the purflings by round about 0.10 mm to 0.13 mm. The exact amount with your glue system must me determined by experiment.</p>

<p>2. Bending needs water applied to the strips. Water swells wood. How much? Measure your purflings before and after bending.</p>

<p>3. Veneer tends to buckle when glue is applied on one side only.</p>

<p>4. Purfling strips also tend to curl and bluckle when different woods and different thicknesses are glued together.</p>

<p>5. Some makers use low-viscostity cyanoacrylate glue after inlaying tiles and purflings. The glue flows into between and under the tiles and veneer strips, and should create a perfect bond. Personnally, I believe that a traditional approach is better here: The liquid diffuses into the soundboard wood and changes its properties. Additionlly, the stability over long periods of time is not proven, as it is with hide glues.</p>

<p>4. Titebond has been successfully used.</p>

<h2>Links</h2>

<p><a href="http://www.cumpiano.com/Home/Classes/Rosette/sandwich.htm">Allan Chapman's tutorial</a> at Cumpiano's workshop.</p>

<p><a href="http://theartoflutherie.com/the-veneer-thicknessing/">Veneer Thicknessing</a> - Art of Lutherie.</p>

<p><a href="http://www.lie-nielsen.com/inlay-tools/">Veneer Thicknesser</a> Lee Nielsen.</p>

<p><a href="http://www.touchstonetonewoods.co.uk/products/classical-guitar-rosettes-289/">Touchstone Tonewoods</a>, preassembled rosettes.</p>

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